arm64: dts: qcom: qcm6490-fairphone-fp5: Add DisplayPort sound support

arm64: dts: qcom: qcm6490-fairphone-fp5: Add DisplayPort sound support

Add the required nodes for sound playback via a connected external
display (DisplayPort over USB-C).

In user space just the following route needs to be set (e.g. using
ALSA UCM):

  amixer -c0 cset name='DISPLAY_PORT_RX Audio Mixer MultiMedia1' 1

Afterwards one can play audio on the MultiMedia1 sound device, e.g.:

  aplay -D plughw:0,0 test.wav

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Link: https://lore.kernel.org/r/20250507-fp5-dp-sound-v4-5-4098e918a29e@fairphone.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>